1. Field of the Invention
The present invention relates to a multiplexed signal transmitting and receiving apparatus which can transmit a wide aspect signal for forming a wider screen than a screen obtained by an image signal processed in each existing television system and which has an improved transmission scheme so that the transmission signal can be received and reproduced even by a television receiver of the existing television system.
2. Description of the Related Art
A television system has been recently studied and developed which can transmit a television signal for a wider screen of an aspect ratio (e.g., 16:9) than a screen of an aspect ratio (4:3) obtained by a television signal of the existing television system while maintaining the compatibility with the existing television system.
This wide aspect signal transmission system can be roughly classified into the side panel scheme and the letter box scheme. These two schemes will be described.
The side panel scheme will be described first.
According to the side panel scheme, an image signal for a screen with an aspect ratio of 16:9 is divided into a center panel signal and right and left side panel signals. The center panel signal is time-expanded in the horizontal direction and set to an aspect ratio of 4:3. The side panel signals are time-compressed and multiplexed on a horizontal over-scanning portion or the like. When the image signal encoded in this manner is reproduced with a television receiver of the existing television system, the center panel is displayed on the entire portion of the screen of the aspect ratio of 4:3. In a decoder for a wide aspect signal, the center and side panel signals are subjected to processing opposite to that in encoding. The center and side panel signals are combined and processed so that an image can be displayed on a screen of an aspect ratio of 16:9. Literature describing the side panel scheme includes "Studies on Multiplex Method for Aspect Ratio Increase", Technical Report of Television Society, August 1989, Vol. 13, No. 41, pp. 19-24.
The letter box scheme will be described.
According to the letter box scheme, an image signal for a screen having an aspect ratio of 16:9 is compressed in the vertical direction and processed so that it can be displayed on a screen of an aspect ratio of 4:3. Upper and lower black bar portions are formed in the upper and lower portions of the conventional display screen due to this compression. A high-resolution signal omitted from the center portion signal is multiplexed on the upper and lower black bar portions and can be utilized when a wide aspect signal is to be decoded. Accordingly, in a decoder, the center portion is vertically expanded, and the high-resolution signal multiplexed on the upper and lower black bar portions is reproduced and added to the vertical expanded image signal. Literature describing the letter box scheme includes "One Method of Improving Vertical Frequency Characteristic by Letter Box Scheme", Technical Report of Television Society, September 1989, Vol. 13, No. 41, pp. 37-42.
As described above, when a signal is transmitted and received by using the side panel or letter box scheme, the encoded television signal has compatibility with the existing television system and can thus be received and reproduced by a television receiver of the existing television system. However, both the side panel and letter box schemes have individual problems.
According to the side panel scheme, the side panels which are cut are not displayed on the television receiver of the existing television system. A program material must be considered on a condition that the side panels will be cut. To cut the side panels also poses a problem in terms of the copyright of the program production.
On the other hand, according to the letter box scheme, the entire wide screen can be displayed on the television receiver of the existing television system. In this case, however, the upper and lower black bar portions occupy the screen at a large ratio, and the utilization efficiency of the entire screen is not good.